Speed governors for a music box or the like are disclosed in exemplary U.S. Pat. Nos. 4,458,573 and 4,464,969. The speed governor is briefly described below while referring to FIG. 6, where a rotary member 61 made of an elastically deformable material such as rubber is provided on a rotatably supported worm shaft 60. It includes weight portions 61a and arm portions 61b coupling the weight portions 61a to the central portion of the rotary member 61. The worm shaft 60 is rotated by a worm wheel 62, which is the final member of a gear train connected to the drum of the music box or the like, which is not shown in FIG. 6. An annular brake member 63 is provided opposing the top of the rotary member 61. When the rotational speed of the worm shaft 60 being rotated by the worm wheel 62 has exceeded a prescribed value, the weight portions 61a of the rotary member 61 elastically deform the arm portions 61b thereof due to the centrifugal force thereon so that the arm portions 61b are moved to positions shown by dotted lines in FIG. 6. The friction surfaces 61c of the arm positions 61b rub the brake member 63 to create a frictional resistance to brake the rotation of the worm shaft 60 and the worm wheel 62, thus keeping the rotational speed of the drum at the prescribed value.
The speed governor disclosed in the U.S. Patents mentioned above utilizes both air resistance and frictional resistance, and has a feature that the governor is capable of securely controlling the speed of the drum of the music box or the like and is single in construction.
When the time (the playing time of the music box or the like) required to rotate the drum thereof by one revolution is to be lengthened, either the air resistance and the frictional resistance are increased or the distance G between the friction surface 61c of each arm portion (61b of the rotary member 61) and the brake member 63 in the stopped state of the speed governor is reduced by altering the press-fit location of the rotary member 61 on the worm shaft 60. However, increasing the air resistance and the frictional resistance creates a problem in that the number of components processed or adjusted for the increased rotational time is large, which makes the work of increasing the rotational time inefficient and makes the cost thereof high. Also, reducing the distance G creates additional problems in that adjustment of the press-fitting equipment for adjusting the final location of the rotary member 61 is time-consuming, which makes the cost of reducing the air gap G high. In addition, the effect of adjustment of the air gap on the rotation time does not produce consistent results, which makes the initial value of the time of every single revolution of the rotation of the drum irregular.